In copending application Ser. No. 751,890 filed Dec. 17, 1976 by one of us, Guglielmo Giacoppo, there has been disclosed a modular connector unit which can be clipped together with other such units to form such a switching frame. Each connector unit is in the form of a flat, generally prismatic housing with banks of input and output terminals for incoming and outgoing lines and with a seat for a junction box within which extensions of these lines are interconnected. As mentioned in that prior application, these line extensions should have terminations that are readily accessible for the purpose of breaking an existing connection or for the insertion of testing equipment into a line. As further described in that application, the line terminations disposed within the junction box are carried on a block which is frictionally or otherwise received in that box and can be extracted therefrom for replacement purposes.